This invention relates to a method and apparatus for measuring vibrations of a rotary shaft.
In a rotating machine such as a pump or the like, for supervising the performance of the rotating shaft, a method of measuring the vibration of the shaft has been used.
For measuring the vibration of the shaft from a remote position and in a noncontact condition, a laser Doppler vibration meter utilizing the light Doppler effect has been used. As shown in FIG. 5, this laser Doppler vibration meter comprises a laser beam generator 1 and the laser beam generated thereby is passed through an optical modulator 2 for dividing the beam into two laser beams B.sub.1 and B.sub.2, one laser beam B.sub.1 being used as an output beam 3 directed to an object 4 to be measured, whereas the other beam B.sub.2 being used as a reference beam.
A beam, reflected by the body 4 which is to be measured, undergoes a Doppler shift corresponding to the vibration speed of the object to be measured and is input to a fiber coupler 7 via a light receiving optical system 6.
The reference beam 9 interferes with the reflected beam 5 in the fiber coupler 7 and an optical fiber, not shown. The output of the fiber coupler 7 is converted into an electric signal by a light receiving element 8. This electric signal is converted into an output representing the vibration speed of the object 4 to be measured by a converter, not shown. By integrating the output of the vibrating speed, the vibration displacement of the object 4 to be measured can be outputted.
By using the prior art Doppler vibration meter described above, the vibration displacement of one point on the rotating shaft can be measured from a remote position in a noncontact condition. However, during this measurement, when the rotating shaft inclines, the measured vibration displacement would contain an inclining error, thus making inaccurate the result of measurement.
Moreover, it is impossible to measure the twisting angle vibration of the shaft and the inclination angle vibration of the shaft. To measure these various vibrations, independent vibration meters must be used. As a consequence, vibration measuring operations become complicated, and the adjustments of various measuring apparatus become difficult.